This invention relates to improvements in current measurement circuits and to an improved current sense resistor for use in such circuits. It is especially related to current measurement in electric power assisted steering systems.
It is well known that the current flowing along a path in an electrical circuit can be measured by measuring the potential drop across a resistor connected in series within the path. Through the application of Ohm's Law the current is given as I=(Vi−Vo)/R where Vi and Vo are the input and output voltages to the resistor in Volts and R is the resistance in Ohms.
The measurement of potential drop is typically made by connecting the input and output side of the resistor to the positive and negative input terminals of a differential amplifier and then to a microprocessor which converts the output of the differential amplifier into a current value if required.
Whilst such circuits are generally reliable, the applicant has appreciated for the first time that there exist a number of possible failure modes and an object of the invention is ameliorate at least one possible mode of failure.